Postconditioning attenuates myocardial ischemia-reperfusion injury by inhibiting complement activation and upregulation of miR-499.

The complement system plays a vital role in myocardial ischemia/reperfusion (I/R) injury. microRNA (miR)-499 is involved in the cardioprotection of ischemic postconditioning (IPostC). The present study aimed to study the role of the complement system and miR-499 in IPostC. Rat hearts were subjected to coronary ligation for 30 min, followed by reperfusion for 2 h. IPostC was introduced at the onset of reperfusion with three cycles of reperfusion for 30 sec and coronary artery occlusion for 30 sec. To study the role of miR-499 in IPostC, adeno-associated virus (AAV) vectors of miR-499-5p (AAV-miR-499-5p) and miR-499-5p-sponge (AAV-miR-499-5p-sponge) were transfected via tail vein injection, followed by IPostC protocols. Cardiac injury as well as the status of local and systemic complement activation and inflammation were assessed. IPostC significantly attenuated I/R-induced rat cardiomyocyte apoptosis and the myocardial infarct size. These beneficial effects were accompanied by decreased local and circulating complement component (C)3a and C5a levels, decreased inflammatory marker expression, decreased NF-κB signaling and increased cardiac miR-499 expression. AAV-miR-499-5p prevented local and systemic complement activation and inflammation as well as enhanced the cardioprotection of IPostC, whereas AAV-miR-499-5p-sponge produced the opposite effects. In summary, IPostC protected the rat myocardium against I/R injury, by inhibiting local and systemic complement activation; inflammation; NF-κB signaling; and upregulation of miR-499. As such, miR-499 may have a critical role in IPostC-mediated cardioprotection against I/R injury.